The wind resistance of sealed asphalt shingles is directly related to the ability of the sealed shingle to resist the force of the wind acting to lift the shingle from the shingle below. This test method employs the measured resistance of the shingle to mechanical uplift after sealing under defined conditions, in a calculation which determines whether this resistance exceeds the calculated force induced by wind passing over the surface of the shingle. Natural wind conditions differ with respect to intensity, duration, and turbulence; while these conditions were considered, and safety factors introduced, extreme natural variations are beyond the means of this test method to simulate.
Many factors influence the sealing characteristics of shingles in the field; for example, temperature, time, roof slope, contamination by dirt and debris, and fasteners that are misaligned or under driven and interfere with sealing. It is beyond the scope of this test method to address all of these influences. The classification determined in this test method is based on the mechanical uplift resistance determined when representative samples of shingles are sealed under defined conditions before testing.
The calculations that support the Classes in 4.1 use several standard building environment factors. These include the 3-s wind gust exposure from ASCE-7, installation on Category I or II buildings for all slopes, ground roughness B or C, and installation on buildings 60 ft tall or less.
Note 28212;The assumptions used in the calculations for the classes in 4.1 cover the requirements for the majority of the asphalt shingle roofs installed. If environmental factors are outside those used in the calculations for these classes, such as ground roughness D, building heights greater than 60 ft tall, building use categories III or IV and other exposures as defined by ASCE-7, other calculations are required. Consult the shingle manufacturer for the specific shingle’s DCp, EI, L, L1, and L2 values needed to complete these calculations.
The test to determine uplift coefficients is conducted with a wind velocity of 15.6 ± 1.3 m/s (35 ± 3 mph). Research data obtained during the development of this test procedure, as well as standard wind modeling practices, provides for data extrapolation to other wind speeds. In order to simulate the raised shingle edge that is inherent behavior under high wind exposure, shims are inserted under the windward edge of the shingle as appropriate based on wind speed and uplift rigidity of the shingle being investigated. This test method provides a means of measuring shingle uplift rigidity which is used to determine the correct shim thickness. Additionally, this test method allows for the use of a default value for uplift rigidity (EI) of 7175 N-mm2 (2.5 lbf-in.2), if a rigidity measurement is not made. This default value is conservative since the lowest EI measured in the development of this program was 14 350 N-mm2 (5.0 lbf-in.2).
Note 38212; The entire field of wind engineering is based on use of small-scale models in wind tunnels using wind speeds much lower than the full-scale values. Building Codes permit testing of this type to replace the analytical provisions of the Building Code through the provisions of ASCE 7. (See Appendix X1 for details and references.)
1.1 This test method covers the procedure for calculating the wind resistance of asphalt shingles when applied in accordance with the manufacturer''s instructions, and sealed under defined conditions. Shingle designs that depend on interlocking or product rigidity to resist the wind cannot be evaluated using this......
Copyright ©2024 All Rights Reserved